# Introduction to energy problem - did I do this right?

## Homework Statement

The bullet strikes a block of wood which exerts, on average, a force of 50,000N opposing the motion of the bullet. How far does the bullet penetrate?

Mass of bullet = 25g
Initial velocity of bullet = 350 m/s
Final velocity of bullet = 0 m/s

## Homework Equations

Ei+work=Ef
K = ½mv^2
Energy = Force * Displacement

## The Attempt at a Solution

Please excuse my attempt of it's egregiously wrong, I was just introduced to energy yesterday; this is one of the first problems I'm doing.

Anyways, because the final velocity of the bullet is zero, the bullet must have lost all of its energy, making Ef=0 J. The bullet initially had kinetic energy, making Ei=K. Thus, my new equation is
K+work = 0 J
½mv^2+work=0 J

I also know that the problem gave me how many Newtons oppose the object, but I need to find out how much energy it used. Since Energy = Force*Displacement, I can rewrite the equation as:
½mv^2+(F*Δx) = 0 J
So I solved it below...
½(.025kg)(350 m/s)^2+(-50000N*Δx) = 0 J
Δx=.03m

Did I do this problem right? If not, what did I do wrong?

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Chestermiller
Mentor
I didn't check your arithmetic, but you methodology is correct.

Chet

haruspex